In the production of extruded materials from synthetic resins or plastics, especially thermoplastic extrusions like vinyl siding composed of polyvinyl chloride, it is common to emboss a pattern on the extruded material.
Consequently, a typical sheet extrusion line as may be used for the production of polyvinyl chloride siding can include an extruder provided with a sheet die capable of extruding as a continuous strand, a hot body or extrusion which is then passed through an embosser before it enters a calibration system and is engaged by a hauler, haul-off or take-off device which draws the extrusion through the calibration and cooling unit.
The embossing unit can include an embossing roller juxtaposed with a backing roller and forming with the backing roller a gap through which the extrusion is passed.
The embossing and backing rollers may be chilled by the circulation of a chilling fluid through them.
In addition, along the extrusion line, the pliable and plastically deformable extrusion may pass around or into contact with one or more chill rollers which also are chilled by the circulation of a liquid through them.
The calibration and sizing unit may comprise one or more calibrators or sizers, referred to as vacuum calibrators or sizers and in which the extrusion is drawn by suction against a calibrating or sizing surface imparting nuances in shape or size to the extruded product.
The calibration table may include a cooling bath or other means for subjecting the extrusion to a cooling fluid whereby the extrusion is rigidified.
Along the line, especially for the production of vinyl siding, any necessary slot and punching devices can be provided and a cutter can be located along the line for subdividing the continuous extrusion into lengths.
In the case of vinyl siding as well, it is possible to provide box-erecting means for forming cartons or the like in which the siding is to be shipped, and means for introducing predetermined numbers of the lengths of siding which are produced into the cartons or boxes thus provided.
The hauler or haul-off device may be a tractor-type hauler in which a pair of endless tracks engages the extrusion between them.
In systems of the aforedescribed type, the rotary embossing unit provides an embossed or textured surface on the extruded product and one or both of the embossing rollers can be driven, e.g. by a motor. The upper roller surface is usually made of steel and carries a reverse of the pattern to be transferred to the plastic extrusion. This upper roller is pressed against the plastic extrusion which are supported by the backing roller.
A rotary embosser should maintain uniform pressure between the cylinders or rolls to control the embossing depth, must operate at a speed which matches the line speed of the extruded sheet, and generally must have its rolls chilled or cooled by the circulation of, for example, chilled water therethrough.
In the past, it has been found to be necessary to change the pattern of the embossed product fairly frequently and, using current technology, this changeover has required between one-half hour and three hours to remove at least the embossing roll, mount a new embossing roll in place and connect up the various liquid fittings which may be required.
The interruption in the line which this changeover requires has, in the past, necessitated the purging of the extruder in the case of polyvinyl chloride siding production. In addition to the down time, there is a loss of material amounting typically to 500 to 1400 pounds, in addition to the loss in output.
Clearly the conventional apparatus which requires such substantial changeover time is a severe economical and technological problem.